Vacuum deposition of coatings using cathode sputtering induced by glow discharges is currently in widespread use. Sputter coating sources include cathode and anode structures, and are operated in an evacuated chamber back-filled with a sputter gas (typically argon at subatmospheric pressure). Positive ions formed in the space between anode and cathode impact a target located on the cathode surface, ejecting (by sputtering) atoms of target material from the surface and near subsurface atomic layers of the target. These sputtered atoms deposit on workpieces or substrates placed generally in line of sight of the target. Magnetron sputter coating sources employ magnetic fields crossed with electric fields in the vicinity of the target. The use of such magnetic fields can enhance glow discharge intensities and the attendant sputtering rates, extend operation to lower sputter gas pressures, confine the glow discharge to the neighborhood of the electrodes, and reduce electron bombardment of the substrates.
One type of magnetron sputter coating source in commercial use employs a nonmagnetic annular sputter target (cathode) of a generally inverted conical configuration surrounding an axially symmetric central anode. One example of such a sputter coating source may be found described in U.S. Pat. No. 4,100,055, issued July 11, 1978 to Robert M. Rainey and entitled "Target Profile For Sputtering Apparatus" and assigned to the assignee of the present invention. A second example of such a sputter coating source is described in detail in co-pending application U.S. Ser. No. 150,532 filed May 16, 1980 in the name of the present inventor and entitled "Magnetically Enhanced Sputter Source" and assigned to the assignee of the present invention.
In most sputter coating applications, the material being deposited is nonmagnetic, such as aluminum and its alloys, etc. In some cases, however, it is desired to use the same sputter coating sources to dispense such magnetic materials as iron, nickel, iron-nickel alloys, etc., as well as the nonmagnetic materials for which the sputter coating sources were initially designed. Simply replacing a nonmagnetic sputter target with a magnetic sputter target of the same generally inverted conical configuration in the magnetron sputter coating sources referred to above would result in shunting most of the magnetic field through the magnetic target. This would result in magnetic fields above the target being too low to allow the desired magnetic enhancement of the glow discharge to take place.
In order to avoid excessive reduction in magnetic field intensities above the target, annular magnetic sputter targets of a generally L-shaped profile have been developed for use in the first of the above-described sputter coating sources. One such L-shaped magnetic sputter target is described in U.S. Pat. No. 4,060,470, issued Nov. 29, 1977 to Peter J. Clarke and entitled "Sputtering Apparatus And Method" (see FIG. 9). An essential feature of the L-shaped designs is that the radial thickness of the outer annular band portion must be sufficiently thin that it is magnetically saturated in order that the magnetic field intensities above the target can be made sufficiently great that the desired magnetic enhancement of the glow discharge takes place. The higher the saturation magnetization of the material, the thinner the annular band portion must be.
Magnetic sputter targets having an L-shaped profile contain much less material than nonmagnetic sputter targets of a generally inverted conical configuration. Moreover, the magnetic fields above the L-shaped magentic targets lead to target erosion which is concentrated in the corner region. In relative terms the amount of magnetic target material usefully available for sputtering is therefore very limited.
It is also known that if magnetic material is heated to or above its Curie temperature, it loses its magnetic properties. Thus, another approach for avoiding reduction in magnetic field intensities above the target would be to heat the target to its Curie temperature at which the target material loses its magnetic property. A disadvantage of this approach is that it requires means for monitoring the temperature of the target, coupled with a feedback system for achieving and maintaining the required Curie temperature. Also, the Curie temperature of some magnetic materials is so high as to be detrimental to the adjacent substrate being coated and/or to the vacuum seals for the system and/or to cause damage to the sputter coating source or target as a result of excessive thermal expansion.
Accordingly, it is an object of the invention to provide improved magnetic sputter target designs in which the amount of magnetic target material usefully available for sputtering is greatly increased over the prior art targets and avoids the temperature monitoring and controlling requirements and other disadvantages of the Curie temperature approach.
A further object of the invention is to provide an improved magnetic sputter target design which is capable of dispersing relatively large amounts of magnetic target material for a variety of target shapes, including annular targets and planar targets.
Another object of the invention is to provide the improved magnetic target designs in configurations which will fit exactly the same magnetron sputter coating sources and be cooled in exactly the same manner as nomagnetic targets fit and are cooled by such sources, whereby the same coating sources can be used with both magnetic and nonmagnetic targets.